Exogone (Exogone) koorenborongi, Guillermo San Martin, 2005

Guillermo San Martin, 2005, Exogoninae (Polychaeta: Syllidae) from Australia With the Description of a New Genus and Twenty-two New Species, Records of the Australian Museum 57, pp. 39-152 : 139-140

Exogone (Exogone) koorenborongi n.sp.

Fig. 87A–K

Material examined. AUSTRALIA: WESTERN AUSTRALIA. HOLOTYPE: AM W26617, south east end of Long Island, Goss Passage, 28°28.8'S 113°46.5'E, dead coral covered in coralline algae, 8 m, P.A. Hutchings, 22 May 1994. PARATYPES: 2 specimens, AM W26618, south east end of Long Island, Goss Passage, 28°28.8'S 113°46.5'E, dead coral covered in coralline algae, 8 m, P.A. Hutchings, 22 May 1994. PARATYPE: 1 specimen, AM W26619, south east end of Long Island, Goss Passage, 28°28.8'S 113°46.5'E, dead coral covered in coralline algae, 8 m, P.A. Hutchings, 22 May 1994.

Description. Body small, slender, filiform, 3.3 mm long, 0.14 mm wide, 29 chaetigers; lateral lobes of nuchal organs usually dark to black, distinct (Fig. 87A). Prostomium oval; 4 eyes in trapezoidal to rectangular arrangement; antennae minute, inserted close to each other near anterior margin of prostomium, ovoid, median antenna slightly longer than lateral antennae (Fig. 87A). Palps broad, longer than prostomium, fused along their length, with a distinct dorsal furrow, with distal notch (Fig. 87A). Peristomium small, dorsally covered by chaetiger 1; tentacular cirri similar both in shape and length to antennae. Dorsal cirri ovoid, longer than antennae, shorter than parapodial lobes or similar in length, present on all segments (Fig. 87A). Anterior parapodia each with 1 compound chaeta, shaft distally provided with long spines of which one distinctly longer, and short, smooth, unidentate blade, about 18 µm long (Fig. 87D); in addition 3 falcigers with spinose shafts and short, smooth blades, with distal tooth indistinct and long subdistal tooth (Fig. 87E), about 4–5 µm long. Midbody parapodia each with solitary compound spiniger-like chaeta, similar to those of anterior parapodia (Fig. 87F), and 2 compound falcigers with spinose shafts, one spine longer than others, and blades short, usually one of them provided with very small distal tooth and one without distal tooth (Fig. 87G). Posterior parapodia each with a single spiniger-like compound chaeta, similar to those of midbody (Fig. 87J) and solitary compound falciger, with blade short, smooth and without distal tooth (Fig. 87K). Dorsal simple chaetae from anterior parapodia, with rounded tips and finely spinulose subterminally, thicker posteriorly (Fig. 87C,H). Ventral simple chaetae on posterior parapodia, thick, sigmoid, bidentate, subdistal tooth long and broad, distal tooth small (Fig. 87I). Pygidium semi-circular, with 2 short anal cirri, longer than dorsal cirri (Fig. 87B) and a distal papilla. Pharynx through 2 segments; pharyngeal tooth on anterior rim (Fig. 87A). Proventricle small, occupying only one segment, nearly rounded, with about 12 muscle cell rows.

Remarks. This species is characterized by its small size, minute, papilliform antennae located on anterior margin of prostomium and short proventricle. The dark lateral lobes of the nuchal organs (see Lewbart & Riser, 1996) are more distinct in some specimens and almost indistinct in others.

Exogone (E.) koorenborongi n.sp. is similar to Exogone (E.) goorapuranga , described above; that species, however, has a longer median antenna, lacks spiniger-like compound chaetae on anteriormost parapodia, and the chaetae, both compound and simple, are different. Also Exogone (E.) koorenborongi is similar to Exogone (E.) naidina , and it is possible that some records of that species in Australia should be referred to Exogone (E.) koorenborongi .

Distribution. Australia (Western Australia).

Habitat. Inside dead corals, 8–30 m depth.

Etymology. The specific name comes from combining two Aboriginal words: kooren meaning neck, and borongi meaning dark, in reference to the dark lobes of the nuchal organs.